It is known in belt technology that tension-member systems can be embedded into a surrounding belt material in order to absorb tensile powers and in order to provide reempowerment. The belt material of the belt base is often composed of synthetic or other rubber, or of other polymers. Tension-member systems often used comprise cables made of synthetic fibers or steel, another term used for these in this connection being cord. A cable or cord can have been formed by various processes, which can involve one or more combined-group-twisting (laying) or braiding processes. Irrespective of the structure of the cable, a feature of all cords is that there are interstices within the volume of the cord. The manner of filling of said interstices greatly affects the properties of the tension-member system.
U.S. Pat. No. 3,138,962 B discloses a power-transmission belt in which, during the casting of the molding of the belt structure, the cord interstices are completely filled by a liquid castable polyurethane into which the cord is embedded. Although this initially leads to good binding of the cord into the material, there is a marked reduction of the lifetime of the belt under load. The belt urethane generally has a high coefficient of friction, and this type of polyurethane as fill material for the cord therefore leads to a loss of elasticity, to low flexibility, and to cord strand breakage caused by stiffening. This effect is particularly marked for carbon fibers and aramid fibers, since these are fine and are easily broken under load if they cannot slip over one another to a certain extent.
EP 0 841 500 B1 discloses a toothed belt made of an elastic polyurethane material which has tension members made of carbon-fiber cord, where the polyurethane material of the belt base penetrates into only a portion of the cord interstices, at least with about 0.2 mg of belt material per mm 3 of cord volume. The carbon cord can already have a size applied by the producer and made by way of example of an epoxide, the intention here being to prevent breakage of the fibers but not to seal the cord completely, but instead to leave spandrel-shaped interstices. A disadvantage is that the cord is bonded purely mechanically into the surrounding belt polyurethane, which retains its high coefficient of friction and has no contact to any other binding material.
In contrast, WO 2011/068729 A1 discloses that a tension-member system which has been embedded into the elastic structure of a belt and which by way of example can be a carbon cord can be provided with urea-crosslinked polyurethane impregnation that fills from 20 to 99% of the interstitial volume, and that the cord thus pretreated can then be embedded into an elastomeric belt structure. The polyurethane cast around the cord here can flow into the remaining interstices. The fill material made of urea-crosslinked polyurethane is produced via crosslinking of a polyurethane prepolymer with diamines or water. The specific fill material is intended to protect the cord fibers from breakage and give the entire cord substantially better elasticity and good flexural properties. A disadvantage is that the fill material for the cord interstices is cured separately prior to the embedment process and therefore does not bond fully satisfactorily to the surrounding belt elastomer.